The present invention relates to electroluminescent (EL) devices having diarylanthracene ladder polymers.
Electroluminescent (EL) devices such as light emitting diode (LED) are opto-electronic devices which radiate light on the application of an electrical field. Organic materials including both polymers and small molecules have been used to fabricate LEDs. LEDs fabricated from these materials offer several advantages over other technologies, such as simpler manufacturing, low operating voltages, and the possibility of producing large area and full-color displays. Organic polymers generally offer significant processing advantages over small molecules especially for large area EL display because polymer films can be easily produced by casting from solutions.
Conjugated polymers are a class of polymers that possess an extended xcfx80-bond network along polymer main chain. Their electronic states can delocalize caused by the effect of the electron-lattice and electron-electron interactions. Conjugated polymers such as poly(p-phenylvinylene) (PPV) were first introduced as EL materials by Burroughes et al in 1990 (Burroughes, J. H. Nature 1990, 347, 539-41). EL efficiency has been improved by balanced electron-hole injection, charge transport, and recombination of the charge carriers. Other conjugated polymers such as polydialkylfluorene (PF) (Ohmori, Y. et al Jpn. J. Appl. Phys. Part 2 1991, 20, L1941), poly(p-phenylene) (PPP) (Grem, G. et al Adv. Mater. 1992, 4, 36), and poly(thiophene) (Ohmori, Y. et al Solid State Commun. 1991, 80, 605) have also been studied.
The light-emitting layer of an EL device comprises a highly luminescent material where electroluminescence is produced as a result of electron-hole pair recombination in this region. In order to achieve efficient light output, efficient and highly fluorescent materials are required. 9,10-Diaryl substituted anthracenes are well known for their high fluorescence efficiency. The highly efficient light output and high operational stability of EL devices have been disclosed in commonly assigned U.S. Pat. Nos. 5,935,721 and 5,972,247 by using substituted diarylanthracenes as light-emitting materials. Ladder polymers containing diarylanthracene moiety are interesting new EL materials. Ladder type xcfx80-conjugated polymers possess outstanding optoelectronic properties, thermal and chemical stability, low concentration of defects, and high intrachain order due to their planar structure (Huber et al. Acta Polymer, 1994, 45, 244)
It is an object of the present invention to provide new luminescent polymeric materials useful for polymer EL devices.
It is a further object of the present invention to provide various energy band gap luminescent polymers which emit broad range of color.
A new class of diarylanthracene-based ladder polymers has been discovered for use in electroluminescent devices.
These objects are achieved in an organic light emitting diode having an anode, a cathode and an emissive layer disposed between the anode and cathode, the emissive layer including the following repeating unit which is used to form a homopolymer or a copolymer comprising the structure: 
wherein:
0xe2x89xa6x less than 1, 0 less than yxe2x89xa61, and x+y=1;
S and T are each independently a chemical bond, an oxygen or sulfur atom, or Cxe2x80x94R, or Nxe2x80x94R wherein C is a carbon atom, N is a nitrogen atom, and R is a substituent including hydrogen, alkyl group of from 1 to 24 carbon atoms, or aryl or substituted aryl of from 6 to 28 carbon atoms, or heteroaryl or substituted heteroaryl of from 4 to 40 carbons, or a cyano group, a nitro group, a chlorine, bromine, or a fluorine atom;
In each ring, including D and E, if either D or E is a single bond, then the other group is not a single bond and is Rxe2x80x94Cxe2x80x94R, wherein C is a carbon atom and R is a substituent as defined above;
Ar1, Ar2, and Ar are each individually aryl or substituted aryl of from 6 to 40 carbon atoms; or
Ar1, Ar2, and Ar are each individually substituted heteroaryl or unsubstituted heteroaryl having 4 to 40 carbons.
The present invention provides light-emitting materials with a number of advantages that include good solubility, efficiency, and stability, low concentration of defects, and high intrachain order. The emitting color of the polymer can be easily tuned by the incorporation of desired Ar group. Furthermore, other electro-optical properties can also be tuned with Ar group. The materials from the present invention can also be used as host materials for other light emitting materials, or as dopants for other suitable light emitting materials.